Strain and Piezo-Doping Mismatch Between Graphene Layers

Modulation of electronic properties of bilayer materials through the strain and doping mismatch between layers opens new opportunities in 2D material straintronics. We present here a new approach allowing to generate asymmetric strain or doping between layers and a method to quantify it using a supported isotopically labeled bilayer graphene studied by in situ Raman spectroscopy. Strain differences up to similar to 0.1% between the two graphene layers have been obtained by applying pressures of up to 10 GPa with nonpolar solid environments. However, when immersed in a liquid polar environment, namely, a mixture of ethanol and methanol, a piezo-doping mismatch between layers is observed. This asymmetrical doping increases with pressure, leading to charge concentration differences between layers of the order of 10(13) cm(-2). Our approach thus allows disentangling strain and doping effects in high-pressure experiments evidencing the asymmetries of these phenomena and comforting isotopic bilayer graphene as a benchmark system for the study of asymmetric effects in devices or composite surfaces.